Weighing the utility of nuclear weapons has always been more theology than science. That was made clear again Tuesday when the House Armed Services Committee’s strategic forces subcommittee poked into the need to spend $10 billion or more improving the Pentagon’s existing arsenal of B61 nuclear bombs.

The advocates of a reliable, potent and fresh nuclear deterrent argue that investing in a retooled B61 is a good use of scarce taxpayer dollars. Those less inclined to spend money on nuclear weapons no one ever wants to see used suggest newer B83s can do the job for at least the next decade. They are the only two bomber-dropped gravity bombs left in the U.S. atomic arsenal.

Not surprisingly, the representatives from the Pentagon and the Department of Energy, which builds the nation’s nukes, support the modernization plan. “This B61 weapon arms the B-2,” Air Force General Robert Kehler, chief of the U.S. Strategic Command, said. “It will arm the future long-range strike platform. It arms the current dual-capable aircraft that are forward stationed in Europe as well as those of our NATO allies that maintain dual-capable aircraft. And it’s the candidate weapon to arm the F-35 in that dual-capable aircraft role.”

The B83 won’t do, Kehler said. It doesn’t work with as many kinds of aircraft, and frankly, it’s just too destructive.

“It has a very high yield,” he said, referring to the size of the explosion it would create. “And we are trying to pursue weapons that actually are reducing in yield because we’re concerned about maintaining weapons that would have less collateral effect if the President ever had to use them.”

Kehler acknowledged fretting about collateral damage in a nuclear war sounds strange. “However, there is a direct relationship between yield and collateral damage,” he added. “Without getting too Strangelovian here…the [B83] weapon is not as flexible as the B61…in terms of our ability to use various yields that would be matched to the targets.”

The B83, truth be told, is a city-destroyer. First detonated in 1984, its yield (adjustable, but about a megaton) is 75 times that of the “Little Boy” that destroyed Hiroshima. The B61 also sports an adjustable yield, but it ranges from a much more modest 0.3 to 340 kilotons, no more that a third of the B83’s punch. In the nuclear realm, that makes it more of a threat — because of its smaller yield, it is more likely to be used — and consequently generates more deterrence.

Kehler said the nation needs an improved B61 to bolster the chances that it will never be detonated. “The ultimate objective of the nuclear deterrent is to make sure that the weapons are never used. And yet, we use them every day to do that,” he said. “It’s almost counterintuitive from people who aren’t informed, but we use those weapons every single day.”